For Q31 - you would redraw the circuit from p to Q to see the differnet path where the current would go. This would cause the circuit to split at the first junction, where one route will go through 4R then directly to Q, and the other path would go to R. After this point (following the path from R) it will split again to a 3R and 6R route and then meet up again, just befote the final R resistor then going back to Q.

You should have have the 3R and 6R resistor in parallel, and so you add them together using 1/Rt = 1/R1 +1/R2 and you will get 2R. This 2R should be in series to the two R resistors, so you add them together to get 4R. Finally this 4R resistor is in parallel to to the other 4R resistor (wich goes directly to Q) and so you add these together and you should get 2R

(Original post by JackSpinner1)
For Q31 - you would redraw the circuit from p to Q to see the differnet path where the current would go. This would cause the circuit to split at the first junction, where one route will go through 4R then directly to Q, and the other path would go to R. After this point (following the path from R) it will split again to a 3R and 6R route and then meet up again, just befote the final R resistor then going back to Q.

You should have have the 3R and 6R resistor in parallel, and so you add them together using 1/Rt = 1/R1 +1/R2 and you will get 2R. This 2R should be in series to the two R resistors, so you add them together to get 4R. Finally this 4R resistor is in parallel to to the other 4R resistor (wich goes directly to Q) and so you add these together and you should get 2R

(Original post by sjaan)
I thought that the new spec of science is linear. Meaning you do all three exams in your third year.What are these exams for?Are they simply exams which you do in order to get predicted grades which don't count towards your actual grade or what?

It's 3 exams to get an A level in physics, and those three exams need to be sat at the same time. However you can still get an AS level, by sitting 2 papers. But if you want to get an A level in you must do those exams again along with the third exam.

Absolute uncertainty: The smallest interval you can measure. E.g. On a 30cm ruler the absolute is +/-1mm but when you take a reading there will be an uncertainty on both sides of the ruler so you might have to double the 1mm so +/- 2mm.
If you have repeat readings the absolute uncertainty is the range/2

Also if two values are being added or subtracted the absolute uncertainty is the uncertainties added together then divided by the result of the calculation:
a + b
=
(uncertainty in a + uncertainty in b) / (a + b)

Uncertainty in gradients= (difference between best gradient and worst gradient) / best gradient
You use the error bars on a graph to find these. The best gradient is the line that goes straight through the middle of the error bars and the worst is from the bottom of the bottom error bar to the top of the top error bar.

Uncertainty in y intercepts = (difference in best intercept and the worst intercept)/best intercept

(Original post by Tim73)
Absolute uncertainty: The smallest interval you can measure. E.g. On a 30cm ruler the absolute is +/-1mm but when you take a reading there will be an uncertainty on both sides of the ruler so you might have to double the 1mm so +/- 2mm.
If you have repeat readings the absolute uncertainty is the range/2

Also if two values are being added or subtracted the absolute uncertainty is the uncertainties added together then divided by the result of the calculation:
a + b
=
(uncertainty in a + uncertainty in b) / (a + b)

Uncertainty in gradients= (difference between best gradient and worst gradient) / best gradient
You use the error bars on a graph to find these. The best gradient is the line that goes straight through the middle of the error bars and the worst is from the bottom of the bottom error bar to the top of the top error bar.

Uncertainty in y intercepts = (difference in best intercept and the worst intercept)/best intercept

Hope that makes sense

On a 30cm ruler, Assuming the ruler increments in mm, the total absolute uncertainty would be +/- 1mm.

(Original post by Tim73)
Are you sure? I was told that when taking a reading using a ruler since there are 2 ends to the ruler, each with an uncertainty then there are technically 2 uncertainties so 1mm * 2 = +/- 2mm

Aye, two ends to the ruler. But assuming the ruler increments in mm's (which it may not), then the uncertainty on each end is 0.5mm. Thus the total uncertainty is +/-1mm.

(Original post by sjaan)
I thought that the new spec of science is linear. Meaning you do all three exams in your third year.What are these exams for?Are they simply exams which you do in order to get predicted grades which don't count towards your actual grade or what?

These exams wont count if we continue physics next year, but if we decide to drop it we get an AS. I think it's to make the transition to the linear course more smooth ie not testing all the new course material after 2 years.

(Original post by Someboady)
Hmm, not too sure about that but if the mark scheme accepts it then you'll get the marks. I personally use the rule of half the smallest division being the uncertainty at either end.

Okay fair enough. I've always been taught its the smallest division which is a bit strange. I don't know why there is disagreement about this

(Original post by Tim73)
Okay fair enough. I've always been taught its the smallest division which is a bit strange. I don't know why there is disagreement about this

This is a weird topic. When measuring with analogue (e.g. a ruler), the uncertainty is +-0.5mm (assuming the smallest division is 1mm). This taken into account, you're not 100% certain that you're measuring from 0cm, hence:

(Original post by Someboady)
Aye, this is the total absolute uncertainty. Remember 0.5mm uncertainty at each end.

I've been taught that when using digital equipment the uncertainty is just the smallest division, not halved or anything.